Hello Tammysue and thank you for writing to JustAsk!
I am not sure where you are located, however I do know that each state must have a board of education written set of guidelines for graduation. Please request a copy of these requirements and any addendums, modifications or regulations that would pertain to a student with an IEP. The types of graduation requirements for a student with an IEP may differ depending on the intensity and level of service given to the child.
I suspect that there may be differences from state to state and perhaps even within each state.
I believe that a student has to complete the minimum number of credits in order to graduate HS, even if they are on an IEP. I would call the district office and speak to the Special Education supervisor. S/he will be able to provide with the correct information.